1. Field of the Invention
The present invention relates to a microstrip meandering-line antenna, and more particularly, to a dual-band microstrip meandering-line antenna.
2. Description of the Prior Art
Recently, the demand for antennas in mobile wireless applications has increased dramatically, and there are now a number of land and satellite based systems for wireless communications using a wide range of frequency bands. Accordingly, there is a need for a single antenna operable in two or more separate frequency bands. Typically, an antenna used in a conventional wireless communications system is a quarter-wavelength monopole antenna or a helix antenna. Nevertheless, since the dimensions of both types of antennas are large, it is difficult to use these antennas in a case in which a compact antenna is required. Therefore, the quarter-wavelength monopole antenna or the helix antenna tends to be replaced by other antennas.
Three types of antennas are candidates for using in a wireless communications system: a patch antenna, a ceramic chip antenna, and a microstrip meandering-line antenna. However, the first two types have their own shortcomings. The patch antenna is restricted by its narrow bandwidth. The ceramic chip antenna is difficult to conform to the specific absorption rate (SAR) standard, so it is not suitable for commercial products. In contrast to the these two types of antennas, the microstrip meandering-line antenna has a wider bandwidth, a lower cost, and can easily be integrated into a circuit board without an additional welding process, giving it the highest potential to be employed in the wireless communications system.
U.S. Pat. No. 5,892,490 discloses a microstrip meandering-line antenna as shown in FIG. 1. FIG. 1 is a perspective view of a microstrip meandering-line antenna 10 according to this prior art. The prior art microstrip meandering-line antenna 10 comprises a substrate 12, a meandering-line conductor 14 disposed inside the substrate 12 for transmitting and receiving radio signals, and a feeding terminal 16 for applying a voltage to the meandering-line conductor 14. Although the microstrip meandering-line antenna 10 has a wider bandwidth and a lower cost, it has only a single resonant frequency. Thus, the meandering-line antenna 10 cannot satisfy the requirement for a dual-band or multi-band wireless communication apparatus.
In addition, EP 0 777 293 A1 discloses a dual-band microstrip meandering-line antenna as shown in FIG. 2. FIG. 2 is a perspective view of a microstrip meandering-line antenna 20 according to this prior art. Differing from the meandering-line antenna 10, the meandering-line antenna 20 comprises two meandering-line conductors 22a, 22b disposed on two different layers of a substrate 24 so as to resonate within two different frequency bands.
However, since the two meandering-line conductors 22a, 22b are disposed on the two different layers of the substrate 24, the meandering-line antenna 20 is complicated and requires a complex manufacturing process. In general, a conductor, which receives radio signals, cannot be disposed near a high frequency circuit due to mutual interference. That is, a distance d1 shown in FIG. 2 must be quite large. Moreover, under the restriction of the two-layer structure, a distance d2 for separating the two layers should be large as well. Therefore, the physical size of this antenna is difficult to shrink.
Additionally, as the resonant frequency is lowered, the corresponding wavelength is lengthened. As a result, the length of the antenna is required to be extended. Therefore, for using a low resonant frequency in the meandering-line antenna 20, the lengths of the two meandering-line conductors 22a, 22b are increased, which adversely affects the current trend towards a thinner, lighter wireless communications system.
It is therefore a primary objective of the claimed invention to provide a dual-band microstrip meandering-line antenna with a meandering-line conductor attached to a surface of a substrate to solve the above-mentioned problems.
According to the claimed invention, a meandering-line antenna for a wireless communications system comprises a substrate having a first surface, a meandering-line conductor, which is attached to the first surface in a reciprocating bent manner for receiving radio signals, having a mid-point connection between two ends of the meandering-line conductor, and a feeding wire electrically connected to the mid-point connection for transmitting a received radio signal to the wireless communications system.
It is an advantage of the claimed invention that the dual-band meandering-line antenna can take advantage of a decreased volume and a simplified structure so as to reduce manufacturing complexity and improve the design.
These and other objectives of the claimed invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment, which is illustrated in the various figures and drawings.